1. Field of the Invention
This invention relates to the processing of tobacco leaf material in the manufacture of smoking articles.
2. Brief Description of Related Art
Tobacco leaves of the types used in the manufacture of cigarettes and like smoking articles comprise leaf lamina, a longitudinal main stem (rib) and veins extending from the main stem. The main stem and large veins are hereinafter jointly referred to as `stem`. The stem has substantially different physical properties from the lamina, and it is long-established practice to separate the stem from the lamina at an early stage in the processing of tobacco leaves, the stem and lamina then being processed independently and differently.
The manner in which stem material is separated from lamina material is generally by means of a complex and large threshing plant comprising a number, eight for example, of serially arranged threshing machines with classification units disposed intermediate next adjacent threshing machines.
As is well known, the separated stem material, or a proportion of it, after suitable reduction in size, is often added back to the lamina after the lamina has been subjected to further processing. Stem material is often desirable in the tobacco blend to improve fill value.
It is general practice in the reduction of stem size for the size reduction to take place when the moisture content of the stem has been raised to a high level of approximately 30-50%, whereas reduction in the size of lamina material is generally undertaken at moisture contents in the region of 18-24%, the precise value depending very much on the type of tobacco, its treatment and the precise cutting conditions.
It is an object of the invention to provide an improved method of processing tobacco leaf material to provide a product suitable for use in smoking articles, cigarettes and cigars for example.
We have looked at ways of simplifying the overall tobacco producing process from leaf to smoking article.
We have found that it is possible to use a mill for the purpose of operating simultaneously on stem and lamina to produce a product useful for incorporation in smoking articles. Whilst we are aware that it has been proposed to use a disc mill to reduce the particle size of stem material on its own, we are not aware of any use of a single mill for simultaneously reducing lamina and stem to a particulate mix of: lamina and stem which is capable of being used for making smoking articles without any substantial further size-reduction process.
Prior proposals for the processing of tobacco leaves to provide filler for cigarettes and like smoking articles are numerous. Examples are to be found in the following patent specifications:
Germany (Federal Republic): 954,136.
New Zealand: 139,007.
United Kingdom: 1855/2134; 413,486; 2,026,298; 2,078,085; 2,118,817; 2,119,220 and 2,131,671.
United States: U.S. Pat. Nos. 55,173; 68,597; 207,140; 210,191; 250,731; 358,549; 360,797; 535,134; 2,184,567; 3,026,878; 3,128,775; 3,204,641; 3,690,328; 3,845,774; 4,195,646; 4,210,157; 4,248,253; 4,323,083; 4,392,501; 4,582,070; 4,696,312 and 4,706,691.